Swimming as part of his rehabilitation from a left knee injury, Nadal said he has been more encouraged recently about his progress and hopes to resume practice soon. He didn't rule out playing next month in the ATP World Tour Finals or Davis Cup final, but added that such a quick return would be difficult.

"I don't want to put any goals to play a tournament," Nadal said Tuesday. "I want to go day by day. I go every day to the gym and the swimming pool to continue with my recovery. I am trying to not think that far."

Nadal spoke from his home in Mallorca during a conference call to promote his participation in an exhibition in New York in March. He has also said he'll enter an exhibition in Abu Dhabi in late December.

The 11-time Grand Slam champion hasn't played since losing in the second round of Wimbledon in June. A partially torn patella tendon forced him to miss the Olympics, where he was the defending gold medalist, and the U.S. Open, where he was the 2010 champion and 2011 runner-up.

After deciding against surgery, Nadal was at first discouraged about how he responded to his rehabilitation regimen.

"I am feeling a little bit better now than the first couple of months," he said. "It has been very, very tough for me because I feel my knee didn't improve in the right direction, but today is something different. The last couple of weeks the improvement of my knee is something I really can feel."

Because of his long layoff, Nadal figures he'll likely need to hit balls for several weeks at least before he returns to competition. The biggest remaining events this year are the ATP World Tour Finals in London Nov. 5-12 and Spain's Davis Cup final against the Czech Republic Nov. 16-18.

"I will need a period of time of practice," he said. "I don't know if that will take a few weeks or one month and a half."

Nadal said he watched "a few matches" during the U.S. Open and felt bad he was unable to take part.

"That's the sport," he said. "That's the negative part of our life."

Nadal, 26, has battled recurring knee trouble for years and finds hard-court matches especially difficult. But he said he can't curtail his playing schedule if he wants to keep contending for a top ranking.

"I can make a few adjustments, but not much," he said. "It's very difficult to think about a completely different calendar for me."